The present invention relates to vehicle conversions and particularly the conversion of a hardtop sedan to a soft-top convertible. Many sedan type automobiles are supplied by the original manufacturer as hardtop automobiles only. A hardtop sedan vehicle provides a generally continuous roof panel which extends from the windshield of the vehicle rearwardly and connects to two rear roof pillars. The rear windshield of the vehicle then extends between the rear roof pillars, above the trunk of the vehicle, and below the continuous top. Side windows extend from the windshield to the rear roof pillars on each side of the vehicle as is well-known. For those automobile models which are not available as a convertible, a post-manufacture conversion can be a way of transforming the vehicle from a hardtop to a convertible construction.
If a vehicle is of a common traditional frame or chassis type construction, the roof can normally be removed with a saw or like tooling. Cosmetic body work then dresses the saw cut areas and a commercially available folding top mechanism manufactured of a steel frame and a fabric covering is added to the vehicle.
Many vehicles are now being manufactured of a frameless unibody construction which does not use the traditional underbody frame or chassis. Such a frame or chassis would normally support the four wheels, the shock absorbers, the engine, and the transmission. The vehicle body parts such as fenders, doors, floor pans, and the like would then be fastened to the chassis. With unibody construction, there is no such vehicle frame. The vehicle unibody typically has a front structural member known as an engine cradle to which the engine and transmission are structurally attached. In the rear of the vehicle, a transverse frame supports the shock absorbers and wheels. It is common to use unibody construction wherein the rear wheels are of an independent suspension in that each wheel functions independently of the other, with each having its own shock tower and strut assembly rather than the traditional rear axial.
With unibody construction, the roof carries an enormous structural load in that it connects to the car adjacent the engine cradle in the front and adjacent the rear transverse support for the shocks and wheels at the rear of the car.
This type construction presents significant problems in converting such a unibody type vehicle to a soft-top convertible. In removing the roof, significant structural integrity of the car is destroyed such as on the order of 50%-80% of the vehicle's body strength. Once the roof is cut away from such a unibody construction, the only support extending between the front wheels and rear wheels of the car is a very thin floor pan. The roof beams and pillars have been destroyed in removing the entire continuous roof panel from the vehicle.
Several of the traditional types of conversions of automobile vehicle bodies have been patented. The Northey patent, for example, entitled "Convertible Car And Method Of Making Same" issued Aug. 31, 1982 as U.S. Pat. No. 4,346,930. In that patent, a hard-roofed two-door Toyota sedan is made into a convertible by removing the hardtop from the car body at the level of the top of the doors. Longitudinal reinforcing tubes are welded into the rocker panels of the vehicle. Reinforcing plates are then welded to opposite sides of the car body at the inside and just above the floor between the rear wheel wells and the door posts. Reinforcing plates are also welded to the sides of the car body at the inside just above the floor immediately in front of the door opening on that side and a pivotal linkage is attached to opposite sides of the car body for operating a convertible top.
In the Draper patent, U.S. Pat. No. 4,457,555, entitled "Conversion Of Vehicles Bodies," a vehicle body of the convertible or targa type is formed by converting a hardtop vehicle body wherein a reinforcing structure is disposed within the passenger compartment and is fastened thereto to form a centrally extending structural channel member extending longitudinally within the passenger compartment and having forward and rear transverse portions fastened to the forward and rearward suspension supports of the body to transmit torsional and beaming loads imposed on the vehicle body by the ground engaging wheels.
The use of reinforcing members on the inside of the vehicle body can cause problems in that the beams can extend upwardly and restrict foot room, thus decreasing the passenger comfort level.
The Monroe et al. patent, U.S. Pat. No. 4,238,876 entitled "Method For Converting Hard Top Vehicles To Removable Top Vehicles" uses a procedure whereby a vehicle which has been manufactured with a top of unitary construction with the body of the vehicle such as a sports pickup truck is converted to a removable hardtop vehicle. This patent relates primarily to the concept of retaining the hardtop, but converting it to a removable structure. The patent includes, however, a step of severing a predetermined portion of the roof of the vehicle from the body of the vehicle thereby exposing a cavity between inner and outer walls of the roof in the vehicle. The Monroe patent differs from the present invention in that a hardtop is thus available for structural integrity to the vehicle once it is reassembled to the vehicle. Further, pickup trucks typically use the traditional heavy frame or chassis construction which is unlike the vehicles converted by the present invention using a frameless, unibody construction having a forward engine cradle to carry the engine and transmission which is separated and spaced from the rear structural transverse frame which supports the rear wheels and shock absorbers.
Another patent relating to the method of converting a sedan or hardtop vehicle to a convertible is the Draper U.S. Pat. No. 4,514,891, entitled "Method Of Conversion Of Vehicle Bodies" issued May 7, 1985. In that patent, the method of converting a sedan passenger automobile includes adding a reinforcing structure having a channel member with inverted U-shaped cross-sections centrally and longitudinally within the interior of the body, fastening the channel member to the floor pan, adding a forward transverse reinforcing member within the interior of the body and fastening it to the channel member, to the floor pan, and to the forward suspension supports. Further, the method contemplates adding a rearward, transverse member to the interior of the body and fastening it to the channel member, to the floor pan and to the rear suspension supports. The continuous roof panel is cut and removed completely from the vehicle and is replaced with a detachable roof panel and a cutaway portion of the continuous panel.
The Deaver patent shows a "Convertible Top Structure And Method" which is U.S. Pat. No. 4,261,615. In that patent, a combined hardtop-soft top conversion structure and method for notchback coupes comprises the removal of rear side glass and rear window, removal of the vehicle just near of the "A" pillar and rear of the inner header structure, with the removal being complete from the top of the "B" pillars to the bottom of the "C" pillars; the attachment of a roll bar to the upper ends of the "B" pillars and gusset reinforcements to the rear of the "B" pillars; capping the roll bar, "B" pillar and gusset reinforcements with a molded plastic bow (sometimes referred to as a `targa` bow); attachment of a folding convertible top to the rear of the `targa` bow; attachment of a front roof support or header to the remaining front roof portion and inner header structure; and insertion of a removable hard roof or hatch support between the front roof support and the front of the `targa` bow.
U.S. Pat. No. 4,570,321 issued Feb. 18, 1986 to David Draper and entitled "Conversion Of Vehicle Bodies" discloses a vehicle body of the convertible or targa type and the method of converting such a body from a sedan type vehicle body in which a reinforcing structure is disposed within the passenger compartment and is fastened thereto to form a centrally extending structural channel member extending longitudinally with the passenger compartment and having forward and rearward transverse portions fastened to the forward and rearward suspension supports of the body to transmit torsional and beaming loads imposed on the vehicle body by the ground engaging wheels.
As aforediscussed, these prior art patents do not relate to an independent four-wheel suspension, unibody type construction which does not use a traditional frame or chassis, but rather only provides a transverse frame at the rear of the vehicle for supporting the rear wheels and shock assemblies and a forward engine cradle for supporting the engine and transmission. The roof panel and pillars on such a vehicle typically supply the majority of longitudinal or fore and aft structural integrity to the vehicle where the roof carries beams and the pillars of the roof carry beams which connect in the rear to the rear transverse member (supporting the wheels and shocks) and in the front to the engine cradle (supporting the transmission and engine).
The use of unibody construction is desirable because it allows a very lightweight and fuel efficient vehicle to be constructed and yet still carry a full passenger load of, for example, five to six (5-6) adults.